This goal of this SBIR project is to quantify the feasibility and potential for an implantable prosthetic device at the distal end of the cut bone for above-knee (AK) amputees. It is hypothesized that such a device can significantly improve residual limb tissue health and load distribution within the prosthetic socket leading to a dramatic improvement in the functional rehabilitation, resultant productivity and overall quality of life of AK amputees. Current surgical techniques for amputation of the distal femur above the knee do not provide an optimum solution for interfacing with a prosthetic socket for weight bearing and ambulation. In order to improve distal weightbearing, reduce rotation of the socket around the residuum and improve clinical function for above-knee amputees, a new surgical method and device is proposed which builds on the long and successful history of joint replacement devices to achieve internal surgical fixation and to gain significant biomechanical advantages compared to current amputation techniques that transversely cut the femur. Most AK amputees are able to achieve only minimal direct skeletal weight transfer at the distal end of the residual limb into socket. The purpose of this development will be to examine the potential for a surgically implanted prosthesis to more simply, elegantly and reliably address the problems of improving the way in which mid-stance weight is transferred from the residual limb of a transfemoral amputee into the prosthetic leg, with the long-term goal of improving pressure distribution, controlling rotation of the residual limb in the socket, and providing significant improvement in prosthesis comfort and function for transfemoral amputees. The key innovation in Phase I will be the development of a practical geometry for a modular prosthetic implant that maximizes pressure distribution and reduces rotation at the distal end of the femur inside a prosthetic socket. The research and development plan in Phase I will consist of the development, prototyping and testing of the implantation methods in laboratory and cadaver models. Technical efficacy will be evaluated by comparing biomechanical measures of pressure distribution in the prosthetic socket and reduction in rotation of the femur in the socket under applied loading conditions for cut bone versus the new prosthetic implant. The long-term goal is to develop a cost-effective implant that can dramatically improve the functional efficiency and quality of life for above knee amputees. The proposed prosthetic implant system provides the enabling technology for improving long term rehabilitation and residual limb health for new and existing transfemoral above-knee amputees. The additional up-front cost of the implant will be far outweighed by reduced health care costs associated with poor socket fit in most above-knee amputees. Increased mobility will come in the form of improved gait speed, increased stability, and reduced energy expenditure, which will also lead to an improved productivity and quality of life. [unreadable] [unreadable]